The human knee joint is a relatively complex articulation of several bones in the leg. It acts as a hinge between the femur (thigh bone) and the tibia (shin bone) and as a gliding articulation between the femur and the patella (knee cap). The articulating surfaces (condyles) of these bones are surrounded by various ligaments, tendons, and cartilage which cushion the bones in the joint and coordinate and guide their movements. Among the ligaments in the knee joint are the lateral and medial menisci. The menisci are approximately semicircular in shape and are posteriorly attached to the tibia, extend transversely to form an extension of the tibial condyles. The menisci are interconnected anteriorly by the transverse ligament.
The menisci are frequently torn or displaced as a result of the application of abnormal forces to either side of the knee. Because each meniscus is peripherally and posteriorly attached to the articulating surfaces of the knee joint, tears may occur anywhere along the perimeter and through the body of the meniscus. Meniscal tears generally extend longitudinally through the body of the meniscus, along lines of hoop stress extending parallel to the circumferential fibers of the tissue. Alternatively, they may extend radially from the inner edge of the meniscus toward the periphery. Meniscal tears may also be obliquely oriented from the inner edge through the body of the meniscus. A torn meniscus may jam or dislocate from between the condyles, causing the joint to lock. Accordingly, a meniscus which has been torn or loosened is generally at least partially excised and removed from the joint.
As opposed to "open" surgery, arthroscopic surgery of the knee involves the placement of several incisions, or portals, in the knee joint region for insertion of various instruments for viewing, grasping, cutting and irrigating tissue. Meniscectomy surgery, the removal of a meniscus or part of one, is generally performed using at least two, and frequently three, portals. One portal is used for insertion of various specialized grasping and/or cutting instruments. A second portal is often used for insertion of an irrigation cannula, and a third portal is often used for insertion of an arthroscope.
Various instruments have been designed to excise torn or damaged meniscal tissue from the knee joint. Meniscectomy instruments are generally highly specialized to grasp and/or cut tissue by shaving, snipping, twisting or nibbling. Some meniscectomy instruments are designed specifically for open surgery while others are designed specifically for arthroscopic surgery.
Some meniscectomy instruments of the prior art feature a guided cutting blade on a track which conforms to the interior of the knee cavity for more precise positioning of the blade. The track may be malleable or flexible to allow manual shaping of the path along which the cutting blade will travel in the guide. For example, U.S. Pat. No. 3,835,859 to Roberts et al. discloses an instrument for complete removal of a meniscus during open surgery having a sliding cutting blade mounted on a flexible guide which is conformed to the interior of the knee cavity by the surgeon. U.S. Pat. No. 3,915,169 to McGuire discloses a surgical knife for removing a meniscus arthroscopically which includes a malleable shank with a blade attached at a distal end thereof. The malleable shank may be manually shaped by the surgeon prior to and during surgery to more precisely position the blade within the incision. In this case, the knife shank is also guided during the procedure by the tissues surrounding the knee joint.
Other meniscectomy instruments may feature a fixed cutting blade track in which a flexible cutting blade is mounted. U.S. Pat. No. 4,067,340 to Le Noir discloses a meniscectomy instrument for open surgery having grooved blade guides formed in the shape of the periphery of the meniscus. The blade guides are located on separate handles which are inserted separately into the open joint and thereafter joined with a cutting blade frame which holds a flexible cutting blade. The cutting blade is held between the grooved blade guides and advances along them, permitting excision of the meniscus along a path described by the grooved guides.
Still other meniscectomy knives may feature multiple cutting blades which are located in precise relationship to one another. U.S. Pat. No. 4,239,045 to Schlein discloses a meniscectomy knife for performing a complete meniscectomy which has two cutting blades fixed at right angles to one another with a guide member located at the intersection of the blades to facilitate insertion and manipulation of the knife. The instrument is curved to conform to the outer shape of the meniscus and has a cutting edge at its forward end. The inner blade also has a cutting edge at its forward end, such that the forward end of the knife presents two cutting edges perpendicularly joined at a common edge.
Meniscectomy knives which are highly specialized for a particular task may require the simultaneous use of additional instruments during meniscectomy surgery, thereby necessitating an increase in the use and number of portals and/or greater involvement by the surgical team. Even meniscectomy knives which have a flexible cutting guide designed for shaping by the surgeon prior to or during surgery may be problematic. It is difficult for the surgeon to anticipate accurately an optimum shape for the cutting guide once the knife is inside the patient. Furthermore, manipulation of a flexible cutting guide during surgery is difficult and cumbersome and may result in a misshapen cutting guide and imperfect excisions of the meniscal tissue. A shaped cutting guide may also change its shape during the surgery as a result of forces exerted upon it during manipulation of the knife within the patient. Furthermore, prior art meniscectomy knives which have a shaped cutting guide and flexible blades, such as the Le Noir knife, or multiple cutting blades, such as the Schlein knife, are also difficult to position precisely within the patient. Neither the flexibility of the cutting blades nor the configuration of the cutting blades on such knives assists the surgeon in placing the instrument within the knee joint at the precise location required for effective excision of any portion of the meniscus.
It is therefore an object of this invention to provide an improved surgical knife useful in excising torn or damaged meniscal tissue from a human knee joint. It is another object of the invention to provide a meniscectomy knife which is anatomically shaped to precisely surround and excise some portion of the meniscus along its circumferential fibers and thus parallel to the lines of greatest stress therein without damaging surrounding nerves, cartilage, blood vessels or ligaments. It is another object of the invention to provide a meniscectomy knife which provides a guided path for excision of portions of the meniscus. It is another object of the invention to provide a meniscectomy knife which may be used with greater versatility in meniscectomy surgery than the prior art instruments, with the objective of minimizing the number of portals required, the types of meniscectomy instruments used, and the extent of surgical team support required. It is another object of the invention to provide a meniscectomy knife which may be easily inserted into and manipulated inside a patient with minimum discomfort or trauma to the patient.